1. Technical Field
The present invention relates to the field of array antennas and more particularly to array antennas having extremely wide bandwidth.
2. Description of the Related Art
Phased array antenna systems are well known in the antenna art. Such antennas are generally comprised of a plurality of radiating elements that are individually controllable with regard to relative phase and amplitude. The antenna pattern of the array is selectively determined by the geometry of the individual elements and the selected phase/amplitude relationships among the elements. Typical radiating elements for such antenna systems may be comprised of dipoles, slots or any other suitable arrangement.
In recent years, a variety of new planar type antenna elements have been developed which are suitable for use in array applications. One example of such an element is disclosed in U.S. application Ser. No. 09/703,247 to Munk et al. entitled Wideband Phased Array Antenna and Associated Methods (hereinafter xe2x80x9cMunkxe2x80x9d). Munk discloses a planar type antenna-radiating element that has exceptional wideband characteristics. In order to obtain exceptionally wide bandwidth, Munk makes use of capacitive coupling between opposed ends of adjacent dipole antenna elements. Bandwidths on the order of 9-to-1 are achievable with the antenna element with the Munk et al. design. Analysis has shown the possibility of 10-to-1 bandwidths achievable with additional tuning. However, this appears to be the limit obtainable with this particular design. Although the Munk et al. antenna element has a very wide bandwidth for a phased array antenna, there is a continued need and desire for phased array antennas that have even wider bandwidths exceeding 10-to-1.
Past efforts to increase the bandwidth of a relatively narrow-band phased array antenna have used various techniques, including dividing the frequency range into multiple bands. For example, U.S. Pat. No. 5,485,167 to Wong et al. concerns a multi-frequency phased array antenna using multiple layered dipole arrays. In Wong et al., several layers of dipole pair arrays are provided, each tuned to a different frequency band. The layers are stacked relative to each other along the transmission/reception direction, with the highest frequency array in front of the next lowest frequency array and so forth. In Wong et al., a high band ground screen, comprised of parallel wires disposed in a grid, is disposed between the high-band dipole array and a low band dipole array.
Wong""s multiple layer approach has a drawback. Conventional dipole arrays as described in Wong et al. have a relatively narrow bandwidth such that the net result of such configurations may still not provide a sufficiently wideband array. Accordingly, there is a continuing need for improvements in wideband array antennas that have a bandwidth exceeding 10-to-1.
An array of radiating elements including a first set of antenna elements in an array configuration and configured for operating on a first band of frequencies, and a second set of antenna elements in an array configuration and configured for operating on a second band of frequencies. The antenna elements can be planar elements having an elongated body portion and an enlarged width end portion connected to an end of the elongated body portion. The enlarged width end portions of adjacent ones of the antenna elements can have interdigitated portions capacitively coupled to corresponding end portions of adjacent dipole elements.
The first set of antenna elements are aligned in a first planar grid pattern of spaced rows and columns and the second set of antenna elements are aligned in a second planar grid pattern of spaced rows and columns, the second grid pattern can be rotated at an angle relative to the first grid pattern, for example 45 degrees.
The first set of antenna elements is positioned below the second set of antenna elements with the first set acting as an effective ground plane for the second set. The array can be configured for wideband operation by having the first band of frequencies adjacent to the second band of frequencies. The array can include a dielectric material interposed between the first plurality of antenna elements and the second plurality of antenna elements.
The array can further include a set of first feed organizers for communicating RF signals to the first set of antenna elements and a set of second feed organizers for communicating RF signals to the second set of antenna elements. The first and second feed organizers are arranged in a common grid pattern and extend upward toward the antenna elements. A set of RF feeds of the second feed organizers form a second feed organizer grid pattern interposed on the common grid pattern. The RF feeds of the second feed organizers extend through a plane approximately defined by the first plurality of antenna elements to communicate RF to the second plurality of antenna elements. A ground plane can be positioned below the first set of antenna elements, and a dielectric layer can be interposed between the ground plane and the first plurality of antenna elements.